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  • McGill University G. Joos1

    Integration and Interconnection of Distributed Energy Resources

    Geza Joos, Professor

    Electric Energy Systems LaboratoryDepartment of Electrical and Computer EngineeringMcGill University

    4 November 2013

    University of Illinois Urbana-Champaign

  • McGill University G. Joos2

    Overview and issues addressed

    Background Distributed generation and resources definition and classification Benefits and constraints

    Grid integration issues

    Grid interconnection and relevant standards Distribution systems standards Steady state and transient operating requirements

    Protection requirements General requirements types of protection Islanding detection

    Concluding comments Distributed energy resources microgrids and isolated systems Future scenarios

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    Electrical power system renewable generation





    Industry Transpor-tation Commercial



    Custom Power



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    Future electric distribution systems a scenario



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    Distributed generation definition classification

    A subset of Distributed Energy Resources (DER), comprising electrical generators and electricity storage systems

    Size from the kW (1) to the MW (10-20) range

    Energy resource Renewables biomass, solar (concentrating and photovoltaic), wind,

    small hydro Fossil fuels microturbines, engine-generator sets Electrical storage batteries (Lead-Acid, Li-Ion) Other fuel cells (hydrogen source required)

    Connection Grid connected distribution grid, dispersed or embedded generation,

    may be connected close to the load center, voltage and frequency st by the electric power system

    Isolated systems voltage and frequency set by a reference generator

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    Distributed generation definition features

    Not centrally planned (CIGRE) is often installed, owned and operated by an independent power producer (IPP)

    Not centrally dispatched (CIGRE) IPP paid for the energy produced and may be required to provide ancillary services (reactive power, voltage support, frequency support and regulation)

    Connection at any point in the electric power system (IEEE) Interconnection studies required to determine impact on the grid May modify operation of the distribution grid

    Types of distributed generation Dispatchable (if desired) engine-generator systems (natural gas,

    biogas, small hydro) Non dispatchable (unless associated with electricity storage) wind,


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    Distributed generation installations

    Typical installations, from large to small Industrial Generating plants on industrial sites, high efficiency, in

    combined heat and power (CHP) configurations Commercial Residential installations, typically solar panels (PV)

    Features of smaller power dispersed generation Can typically be deployed in a large number of units Not necessarily integrated in the generation dispatch, not under the

    control of the power system operator (location, sizing, etc)

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    Distributed generation drivers

    Promoting the use of local energy sources wind, solar, hydro, biomass, biogas, others

    Creating local revenue streams (electricity sales)

    Creating employment opportunities (manufacturing, erection, maintenance, operation)

    Responding to public interest and concerns about the environment public acceptance can be secured

    Green power Greenhouse Gas (GHG) reduction


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    Distributed generation technical benefits

    Enhanced reliability generation close to the load

    Peak load shaving reduction of peak demand

    Infrastructure expansion deferral local generation

    Distribution (and transmission) system loss reduction generation close to load centers

    Lower grid integration costs local generation reduces size of connection to the main grid

    Distribution voltage connection (rather than transmission) ease of installation and lower cost

    Voltage support of weak distribution grids


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    Distributed generation typical installations

    Typical power plant types Hydraulic, 5-10 MW Biomass, 5-10 MW Biogas, 5-10 MW Wind, 10-25 MW

    Total installed power (2011): 61 plants, 350 MW

    Connection: MV grid (25 kV, nominal 10 MW feeders typical for Canadian utilities)


    Ref: Presentation Hydro-Quebec Distribution, 2011

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    Hydro-Quebec on-going projects 2011-2015

    Biomass 4 plants 25 MW on MV grid Commissioning 2012-2013

    Small hydro 8 plants 54 MW on MV grid Commissioning 2010-2013

    Wind power plants 5 plants 125 MW on MV grid Commissioning 2014-2015


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    DG connection to the grid options

    Connection options Distribution network low (LV), typically 600 V, and up to 500 kW Distribution network - medium voltage (MV), up to 69 kV, typically 25

    kV, up to 10-20 MW Transmission network aggregated units, typically 100 MW or more

    Power system impacts Distribution local, typically radial systems Transmission system wide, typically meshed systems

    Differing responsibilities and concerns Distribution power quality (voltage), short circuit levels Transmission stability, voltage support, generation dispatch

    Integration constraints in relation to the electric power grid Power quality should not be deteriorated Power supply reliability and security should not be compromised


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    Integration and interconnection issues

    Integration of the generation into existing grids constraints Operating constraints maximum power (IPP paid for kWh produced),

    desired operation at minimum reactive power (unity power factor) Dealing with variability and balancing requirements (if integrated into

    generation dispatch) characteristic of wind and solar installations Integration into the generation dispatch requires monitoring, energy

    production forecasting

    Interconnection into the existing grid constraints Connection to legacy systems protection coordination, transformer

    and line loading, impact on system losses Reverse power flow from end-user/producer to substation Increased short circuit current DG contribution Operational issues grid support requirements and contribution


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    Specific DG interconnection issues

    Generation power output variability Short term fluctuations flicker (wind, solar) Long term fluctuations voltage regulation, voltage rise at connection

    Reactive power / Voltage regulation coordination Reactive compensation interaction with switched capacitor (pf) Voltage regulation impact on tap-changing transformer operation Impact on Volt/Var compensation interference

    Harmonics and static power converter filter interaction Voltage distortion produced by power converter current harmonics Resonances with system compensating capacitors

    Islanding and microgrid operation Operation in grid connected and islanded modes transfer Microgrids possibility of islanded operation aid to system restoration


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    DG interconnection and control requirements

    Reactive power and power factor control required

    Voltage regulation may be required (using reactive power)

    Synchronization to the electric power system

    Response to voltage disturbances steady state and transient

    Response to frequency disturbances steady state and transient

    Anti-islanding usually required (to avoid safety hazards)

    Fault, internal and external overcurrent protection

    Power quality harmonics, voltage distortion (flicker)

    Grounding, isolation

    Operation and fault monitoring

    Grid support larger units

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    General DG standards

    Distributed resources (DR) standards IEEE 1547, Standard for Interconnecting Distributed Resources with

    Electric Power Systems and applies to DR less than 10 MW

    Generally applicable standards for the connection of electric equipment to the electric grid. IEEE in North America and IEC in Europe, cover harmonic interference

    and electrical impacts on the grid. Most commonly used are the IEEE 519 and the IEC 61000 series.

    Utility interconnection grid codes and regulations issued by regional grid operators as conditions for connecting DGs to the electric grid

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    Operational requirements larger installations

    Based in part on conventional generation (synchronous) may apply to DGs connected to the distribution grid

    Voltage regulation may be enabled

    Frequency regulation may be required

    Low voltage ride through (LVRT) may be required

    Power curtailment and external tripping control may be required

    Control of rate of change of active power ramp rates

    Other features typically required for large wind farms (> 100 MW, transmission connected), may be required for farms > 5-25 MW control of active power on demand reactive power on demand inertial response for short term frequency support Power System Stabilization functions (PSS) special function


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    DG protection issues general considerations

    Operational requirements Distribution system must be protected from influences caused by DG

    during faults and abnormal operating conditions DG must be protected from faults within DG and from faults and

    abnormal operating conditions caused by distribution circuits

    Specific considerations Impact of different DG technologies on short circuit contribution and

    voltage support under faults induction generators, synchronous generators, static power converters (inverters)

    Impact of power flow directionality (reversal) on existing distribution system protection

    Instantaneous reclosing following temporary faults Utility breaker reclosing before DG has disconnected may lead to out-

    of-phase switching avoided by disconnecting the DG during the auto-reclosing dead time (as low as 0.2 s)

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    Protection system role and requirements

    Role to detect and isolate only the faulty section of a system so that to maintain the security and the stability of the system

    Abnormal conditions include effect of short circuits, over-frequency, overvoltages, unbalanced currents, over/under frequency, etc.

    Protection system requirements rated adequately selective will respond only to adverse events within their zones of

    protection dependable will operate when required secure will not operate when not required

    Faults seen by the DG Short circuits on the feeder Loss of mains feeder opening and islanding

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    Protection functions of a DG interconnection




    T1 PCC -LV bus







    Line2 Line3






    DG1 DG2


    PCC -HV bus




    PCCHVside PCCLVside DGLVside

    Distance Automaticrecloser Frequency(overandunderfrequency)Pilotdifferential Fuses Voltage(overandundervoltage)Phasedirectionalovercurrent Voltage(overandundervoltage) Overcurrent(instantaneousanddelayed)Grounddirectionalovercurrent Overcurrent(instantaneous) Lossofmains(islanding)Automaticrecloser Underfrequency SynchronizationUndervoltage Phasedirectionalovercurrent Lossofearth(grounding)Overvoltage Grounddirectionalovercurrent Neutralovercurrent

    Transformerdifferential Negativesequence(voltage,current)Directionalovercurrent ReversepowerflowZerosequence Generator(lossofexcitation,differential)


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    DG islanding detection requirements

    Unintentional islanding defined as DG continuing to energize part of distribution system when connection(s) with area-EPS are severed (also referred to as loss of mains)

    IEEE 1547 - the DG shall cease to energize the Area EPS circuit to which it is connected prior to reclosure by the Area EPS

    Repercussions of an island remaining energized include: Personnel safety at risk Poor power quality within the energized island Possibility of damage to connected equipment within the island,

    including DG (due to voltage and frequency variations)

    Utility grid codes may allow islanded operation during major outages may help restore service in distribution system


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    Islanding detection techniques passive

    Passive approaches Frequency relays (Under/Over-frequency) - use of the active power

    mismatch between island load and DG production levels Voltage relays (Under/Over Voltage) - based on voltage variations

    occurring during islanding, resulting from reactive power mismatch ROCOF relays (Rate Of Change Of Frequency resulting from real

    power mismatch in the case an island is created Reactive power rate of change resulting from reactive power

    mismatch in the case an island is created

    Other approaches Active protection based on difference in area-EPS response at DG

    site when islanded; injection of signature signals at specific intervals Communication-based protection using a communication link

    between DG and area EPS (usually at the substation level) to convey info on loss of mains (and possibly activate a transfer-trip)


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    Alternative approach intelligent relays

    Alternative (intelligent) proposed approach passive, using only measured signals (current, voltage and derived signals)

    Use of a multivariate approach to develop a data base of islanding patterns

    Use of data mining to extract features from the running of a large number of operating conditions (normal) and contingencies (faults)

    Use of extracted features to develop decision trees that define relay settings


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    DG variables monitored multivariable approach


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    Feature extraction methodology

    Data Mining a hierarchical procedure that has the ability to identify the most critical DG variables for islanding pattern detection, or protection handles

    Decision Trees define decision nodes; every decision node uses different DG variables to proceed with decision making on identifying the islanding events

    Training data set islanding (contingencies) and non-islanding events

    Time dependent decision trees generated extracted at different time steps up to the maximum time considered/allowable

    Choice of decision tree for relay setting (best) based on Dependability (ability to detect an islanding event as such) and Security (ability to identify a non-islanding event as such) indices


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    Performance requirements islanding detection

    Requirements - defining maximum permissible islanding detection time (typically 0.5 to 2 s)

    Performance indices Dependability and Security indices Speed of response, or detection time Existence of non detection zones

    Constraints accounting for Interconnection Protection response times (reclosers) detection of islanding and tripping before utility attempts reclosing (out

    of phase reclosing may be damageable)

    Nature of relay and impact on performance requirements short circuit detection needs to be faster that islanding detection allows additional to refine the decision tree


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